It’s not always easy to think of an interesting vegetable side dish for a special dinner. Glazed carrots are a reliable favourite and can be made quickly while your meat is resting, but if you have a little more time, roasted red onions with balsamic vinegar are well worth the effort.
These onions take longer to cook than most sides, but they need very little hands-on work — most of the time is spent quietly caramelising in the oven while you get on with the rest of the meal. The balsamic vinegar reduces down into a sweet, glossy glaze that pairs beautifully with rich meats like lamb or duck.
Ingredients
Serves 6
- 6 medium red onions
- A thin slice of butter
- 1 tbsp olive oil
- A few sprigs of rosemary
- Salt and pepper
- 5 tbsp balsamic vinegar
Method
Preheat your oven to 140°C.
Peel and top and tail the onions. Heat the butter and oil together in a frying pan. Add the onions and sauté for about 5 minutes, until golden. Add the rosemary and season with salt and pepper.
Transfer the onions and rosemary to an ovenproof dish, arranging them right side up. Deglaze the frying pan by adding the balsamic vinegar and scraping up any flavoursome bits stuck to the bottom of the pan, then pour this over the onions.
Cover the dish with tin foil and cook in the preheated oven for 30 minutes. After 30 minutes, remove the foil and continue cooking for a further 1¼ hours. Serve with the juices spooned over the onions.
Cook’s tip: If you’re making these onions to go alongside a roast that’s cooking at 180°C, you can leave the foil on for the first hour, then remove it for the last 30 minutes. Keep an eye on the dish during this time, as you don’t want the balsamic vinegar to evaporate completely. If it does start to dry out, add a little water to the dish and stir it through the vinegar.
Frequently Asked Questions
Can I make roasted red onions with balsamic vinegar ahead of time?
Yes — they reheat well. Cook them fully, cool, and store in the fridge, then warm them through gently in the oven or a covered pan before serving.
What can I serve these onions with?
They’re a lovely match for roast lamb or duck, and work equally well alongside roast beef, pork or a vegetarian roast centrepiece.
Why do the onions need to cook for so long?
The long, slow cooking time is what makes the onions meltingly soft and lets the balsamic vinegar reduce into a rich, sticky glaze. Rushing the cooking time will leave the onions firmer and the sauce thinner.
What if my balsamic vinegar starts to evaporate?
Simply add a splash of water to the dish and stir it into the remaining vinegar to loosen it back up.
More Recipes to Try
If you enjoyed this recipe, you might also like our other simple vegetable side dishes and family-friendly roast dinner ideas — perfect for adding a little extra flavour to your Sunday table.
Save This Recipe
Love a good make-ahead side dish? Bookmark this page or save it to your recipe folder so it’s ready the next time you’re planning a roast dinner.
Get More Family Recipe Ideas
Want more easy, family-friendly recipes delivered straight to your inbox? Sign up for the MyKidsTime newsletter for weekly ideas, recipes and activities for busy parents.
